Thermoplastic composites have excellent strength to weight and elevated use temperature capabilities. The combination of a tough thermoplastic composite face sheet useful in the temperature range between 350.degree. and 400.degree. F., and a stiff environmentally durable titanium honeycomb make thermoplastic coated titanium core panel composites attractive as low-weight and reduced life cycle cost design options. These composites find use in aircraft and space vehicles as high-temperature face sheets on large primary structure panels including, for example, weapons bay doors, avionics doors, cryogenic tanks, and nacelle acoustic panels.
However, attempts to form thermoplastic coated titanium honeycomb panels has proved unsuccessful especially for weight critical applications where low density (e.g., less than 6 lb/ft.sup.3), large cell (e.g., 1/4-3/8 inch), thin foil (e.g., 2.0-2.5 mil) cores are desired. Successful consolidation (e.g., at thermoplastic curing conditions of 665.degree. F. and 185 psi) of certain thermoplastic face sheets to medium density (6 lb/ft.sup.3 and 3/16 cell size) polyimide cores has been accomplished and has been determined to be structurally valid through flatwise tensile, core shear, plate shear, and impact testing. Attempts to co-consolidate thermoplastic panels with titanium honeycomb cores have proved unsuccessful except when using extremely weight inefficient flanged cores. FIG. 1A is a cross-sectional view of a flanged core having cell walls 1 capped with flanges 2. FIG. 1B is a top view of a flanged honeycomb core. Deficiencies that render the use of nonflanged titanium cores ineffective when consolidating thermoplastics at high temperatures and pressures include core crushing, face sheet dimpling, and face sheet ply cutting as illustrated in FIGS. 2A-C, respectively.
As an alternative to panel fabrication by co-consolidation, attempts to fabricate thermoplastic titanium panels have involved preconsolidating the thermoplastic face sheets and then secondarily bonding the consolidated face sheets to the titanium core using a low temperature/pressure (e.g., 350.degree. F. and 45 psi) curing adhesive. A significant drawback to a panel fabricated by this method is that the elevated use temperature (e.g., 350-400.degree. F.) capabilities of such thermoplastic face sheets limits the fabricated panel's environmental regime to that of low temperature bonding adhesive (e.g., about 250.degree. F.).
Accordingly, there exists a need for a thermoplastic titanium honeycomb panel structure that offers the high temperature advantages associated with thermoplastic face sheets and the structural durability of titanium honeycomb. A need also exists for methods for preparing thermoplastic titanium honeycomb panels. The present invention seeks to fulfill these needs and provides further related advantages.